Magnetic resonance diagnosis apparatus, noise spatial distribution generating method, and signal acquisition method

Abstract

A magnetic resonance diagnosis apparatus includes a coil assembly including a high-frequency coil, a transmission unit which excites magnetization of a specific atomic nucleus of an object via the high-frequency coil, a reception unit including a detection unit for receiving a magnetic resonance signal via the high-frequency coil, a low-pass filter, and an analog/digital converter, a control unit which sets a passband of the low-pass filter to not less than three odd multiple of a frequency band determined from an imaging field of view, and sets a sampling frequency of the analog/digital converter to an oversampling frequency exceeding a signal band of the magnetic resonance signal, a noise spatial distribution generating unit which generates a noise spatial distribution on the basis of an output from the reception unit.

1. A magnetic resonance diagnosis apparatus comprising:
 a coil assembly including a high-frequency coil; 
 a transmission unit which excites magnetization of a specific atomic nucleus of an object by driving the high-frequency coil; 
 a reception unit including a detection unit which receives a magnetic resonance signal via the high-frequency coil, a low-pass filter, and an analog/digital converter; 
 a control unit which sets a passband of the low-pass filter to not less than three odd multiple of a frequency band determined from an imaging field of view, and sets a sampling frequency of the analog/digital converter to an oversampling frequency exceeding a signal band of the magnetic resonance signal; and 
 a noise spatial distribution generating unit which generates a noise spatial distribution on the basis of an output from the reception unit. 
 
     
     
       2. The apparatus according to  claim 1 , wherein the control unit sets a passband of the low-pass filter to a band three times a frequency band determined from the imaging field of view, and sets a sampling frequency of the analog/digital converter to a frequency two times the signal band. 
     
     
       3. The apparatus according to  claim 2 , wherein the noise spatial distribution generating unit includes
 a resampling processing unit which generates a first resampled data set and a second resampled data set at different resampling positions from data oversampled by the analog/digital converter, 
 an image reconstruction unit which reconstructs a first image and a second image from the first resampled data set and the second resampled data set respectively, and 
 a difference processing unit which generates the noise spatial distribution by calculating differences between the first image and the second image. 
 
     
     
       4. The apparatus according to  claim 3 , wherein the first image and the second image each is an absolute-value image or a complex image. 
     
     
       5. The apparatus according to  claim 1 , wherein the control unit sets a passband of the low-pass filter to a band three times a frequency band determined from the imaging field of view, and sets a sampling frequency of the analog/digital converter to a frequency three times the signal band. 
     
     
       6. The apparatus according to  claim 5 , wherein the noise spatial distribution generating unit includes
 a resampling processing unit which generates a first resampled data set, a second resampled data set, and a third resampled data set at different resampling positions from data oversampled by the analog/digital converter, 
 an image reconstruction unit which reconstructs a first image, a second image, and a third image from the first resampled data set, the second resampled data set, and the third resampled data set respectively, and 
 a difference processing unit which generates a first noise spatial distribution, a second noise spatial distribution, and a third noise spatial distribution by calculating differences between the first image, the second image, and the third image. 
 
     
     
       7. The apparatus according to  claim 6 , wherein the first image, the second image, and the third image each is of an absolute-value image or a complex images. 
     
     
       8. The apparatus according to  claim 1 , wherein the control unit sets a passband of the low-pass filter to a band three times a frequency band determined from the imaging field of view, and sets a sampling frequency of the analog/digital converter to a frequency four times the signal band. 
     
     
       9. The apparatus according to  claim 8 , wherein the noise spatial distribution generating unit includes
 a resampling processing unit which generates a first resampled data set, a second resampled data set, a third resampled data set, and a fourth resampled data set at different resampling positions from data oversampled by the analog/digital converter, 
 an image reconstruction unit which reconstructs a first image, a second image, a third image, and a fourth image from the first resampled data set, the second resampled data set, the third resampled data set, and the fourth resampled data respectively, and 
 a difference processing unit which generates a first noise spatial distribution by calculating differences between the first image and the third image, and a second noise spatial distribution by calculating differences between the second image and the fourth image. 
 
     
     
       10. The apparatus according to  claim 9 , wherein the first image, the second image, the third image, and the fourth image each is an absolute-value image or a complex image. 
     
     
       11. The apparatus according to  claim 1 , wherein the control unit sets a passband of the low-pass filter to a band three times a frequency band determined from the imaging field or view, and sets a sampling frequency of the analog/digital converter to a frequency n times (n is an integer of not less than two) the signal band. 
     
     
       12. The apparatus according to  claim 11 , wherein the noise spatial distribution generating unit includes
 a resampling processing unit which generates n resampled data sets at different resampling positions from data oversampled by the analog/digital converter, 
 an image reconstruction unit which reconstructs n images from the n resampled data sets, and 
 a difference processing unit which generates the noise spatial distribution by calculating differences between the n images. 
 
     
     
       13. The apparatus according to  claim 12 , wherein the n images each is of an absolute-value image or a complex image. 
     
     
       14. A noise spatial distribution generating method for a magnetic resonance diagnosis apparatus, the method comprising:
 exciting magnetization of a specific atomic nucleus of an object via a high-frequency coil; 
 receiving a magnetic resonance signal via the high-frequency coil; 
 detecting the received magnetic resonance signal by using a detection unit; 
 filtering the detected magnetic resonance signal by using a low-pass filter whose passband is set to not less than three odd multiple of a frequency band determined from an imaging field of view; 
 converting the filtered magnetic resonance signal into digital data by using an analog/digital converter whose sampling frequency is set to an oversampling frequency exceeding a signal band of the magnetic resonance signal; and 
 generating a noise spatial distribution on the basis of the digital data. 
 
     
     
       15. A signal acquisition method for a magnetic resonance diagnosis apparatus, the method comprising:
 exciting magnetization of a specific atomic nucleus of an object via a high-frequency coil; 
 receiving a magnetic resonance signal via the high-frequency coil; 
 detecting the received magnetic resonance signal by using a detection unit; 
 filtering the detected magnetic resonance signal by using a low-pass filter whose passband is set to not less than three odd multiple of a frequency band determined from an imaging field of view; and 
 converting the filtered magnetic resonance signal into digital data by using an analog/digital converter whose sampling frequency is set to an oversampling frequency exceeding a signal band of the magnetic resonance signal.